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HYDRAULIC LIMES AND CEMENTS                   153

2.  Methylene Iodide Test.—This serves to separate the extraneous
matters accompanying a cement and is based on their different densities.
It applies especially to Portland cement and is carried out by shaking a
small quantity of the cement with a solution of methylene iodide in benzene
or oil of turpentine of density 3 i and allowing to stand.   The cement
particles are the heavier and settle, whilst the extraneous matters float.

When a more complete separation is required, methylene iodide solu-
tions of densities 3-05, 3-00, 2-95 and 270 are successively used. What
sinks in the first solution consists of pure Portland cement ; that of density
between 3 and 3-05 is not quite pure cement, that between 2-95 and 3
is mixed cement and slag, and that between 270 and 2-95 pure slag ;
that floating in the solution of density 270 may be coal, ash, gypsum, and
the like. The separate fractions may be examined to ascertain their nature.

3.  Specific Gravity.—This may be determined with the picnometer,
using benzene or benzine as liquid.    Use is also largely made of Schumann's
volumenometer, which consists of a bottle, in the neck of which is ground
a glass tube graduated in tenths of a c.c.   The bottle is filled with the
benzene or benzine to the commencement of the graduation and the division
to which the liquid reaches read ;  TOO grams of cement (or lime) are then
introduced into the bottle, which is tapped gently to make the air-bubbles
rise, the new level of the liquid being then read.

A more convenient volumenometer is that of Le Chatelier, which com-
prises a bulb of about 120 c.c. capacity, terminated by a neck 0-20 metre
high with an expansion measuring exactly 20 c.c. between two marks ;
above the upper mark the tube is graduated from o to 3 c.c. in tenths.
When the apparatus is full of benzene to the lower mark, a definite weight
of the cement (64 grams of Portland cement may be used or 60 grams or
less of a lighter product) is introduced by means of a funnel reaching just
below the upper mark. The increase in volume represents the volume
occupied by the cement.

According to the Official Italian Regulations and Conditions,* the specific
gravity (absolute density) of hydraulic agglomerants may be determined by
any method provided it allows of an accuracy of two units in the second decimal
figiire ; it should be determined on the material after previous drying and powder-
ing so as to pass through a sieve of 900 meshes per sq. cm., and the temperature
of the apparatus, material and liquid during the determination should be
about 15°.

4.  Apparent Density.—This is the weight of a litre of the material
poured without compressing.   To determine it, the cement is gradually
introduced through a funnel into a litre cylinder 10 cm. high until the
cylinder is not only completely filled but heaped up.   The excess is then
removed by drawing a straight strip, held vertically, across the top of the
cylinder, which is then weighed.   The weight thus found, less the tare,
gives the apparent density.

According to the Official Regulations (Italian) already mentioned, the funnel
to be used for filling the cylinder is 20 mm. in diameter at the base and 150 mm.

* The density of methylene iodide is 3-33 at the ordinary temperature.

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